CD14 is a 55 kDa cell surface glycoprotein that is preferentially expressed on monocytes/macrophages. The mouse CD14 cDNA encodes a 366 amino acid (aa) residue precursor protein with a 15 aa signal peptide and a C-terminal hydrophobic region characteristic for glycosylphosphatidyinositol (GPI)-anchored proteins. Mouse CD14 has five potential N-linked glycosylation sites and also bears O-linked carbohydrates. The amino acid sequence of mouse CD14 is approximately 65% and 82% identical to the human and rat proteins, respectively. CD14 is a pattern recognition receptor that binds lipopolysaccharides (LPS) and a variety of ligands derived from different microbial sources. The binding of CD14 with LPS is catalyzed by LPS-binding protein (LBP). The toll-like-receptors have also been implicated in the transduction of CD14-LPS signals. Similar to other GPI-anchored proteins, soluble CD14 can be released from the cell surface by phosphatidyinositol-specific phospholipase C. Soluble CD14 has been detected in serum and body fluids. High concentrations of soluble CD14 have been shown to inhibit LPS-mediated responses. However, soluble CD14 can also potentiate LPS response in cells that do not express cell surface CD14.